Ultrasound-mediated blood-brain barrier opening enhances delivery of therapeutically relevant formats of a tau-specific antibody

A narrative review: Ultrasound-Assisted drug delivery: Improving treatments via multiple mechanisms

Safe and efficient drug delivery is as important as drug development. Biological barriers, such as cell membranes, present significant challenges in drug delivery, especially for newly developed protein-, nucleic acid-, and cell-based drugs. Ultrasound-mediated drug delivery systems offer a promising strategy to overcome these challenges. Ultrasound, a mechanical wave with energy, produces thermal effects, cavitation, acoustic radiation, and other biophysical effects. Used alone or in combination with microbubbles or sonosensitizers, it breaks biological barriers, enhances targeted drug delivery, reduces adverse reactions, controls drug release, switches on/off drug functions, and ultimately improves therapeutic efficiency. Various ultrasound-mediated drug delivery methods, including transdermal drug delivery, nebulization, targeted microbubble destruction, and sonodynamic therapy, are being actively explored for the treatment of various diseases. This review article introduces the principles, advantages, and applications of ultrasound-mediated drug delivery methods for improved therapeutic outcomes and discusses future prospects in this field.

Effects of blood-brain barrier opening using ultrasound on tauopathies: A systematic review

Blood-brain barrier opening with ultrasound can potentiate drug efficacy in the treatment of brain pathologies and also provides therapeutic effects on its own. It is an innovative tool to transiently, repeatedly and safely open the barrier, with studies showing beneficial effects in both preclinical models for Alzheimer's disease and recent clinical studies. The first preclinical and clinical work has mainly shown a decrease in amyloid burden in mice models and in patients. However, Alzheimer's disease pathology also encompasses tauopathy, which is closely related to cognitive decline, making it a crucial therapeutic target. The effects of blood-brain barrier opening with ultrasound have been rarely assessed on tau and are still unclear.

METHODS

This systematic review, conducted through searches using Pubmed, Embase, Web of Science and Cochrane Central databases, extracted results of 15 studies reporting effects of blood-brain barrier opening using ultrasound on tau proteins.

RESULTS

This review of the literature indicates that blood-brain barrier opening using ultrasound can decrease the extent of the tau pathology or potentialize the effect of a therapeutic drug. However, selected studies report paradoxically that blood-brain barrier opening can increase tau pathology burden and induce brain damage.

DISCUSSION

Apparent discrepancies between reports could originate from the variability in protocols or analytical methods that may impact the effects of blood-brain barrier opening with ultrasound on tauopathies, glial populations, tissue integrity and functional outcomes.

CONCLUSION

This calls for a better standardization effort combined with improved methodologies allowing between-studies comparisons, and for further understanding of the effects of blood-brain barrier opening on tau pathology as an essential prerequisite before translation to clinic.

Lipid nanoparticles and transcranial focused ultrasound enhance the delivery of SOD1 antisense oligonucleotides to the murine brain for ALS therapy

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease with extremely limited therapeutic options. One key pathological feature of ALS is the abnormal accumulation of misfolded proteins within motor neurons. Hence, reducing the burden of misfolded protein has emerged as a promising therapeutic approach. Antisense oligonucleotides (ASOs) have the potential to effectively silence proteins with gain-of-function mutations, such as superoxide dismutase 1 (SOD1). However, ASO delivery to the central nervous system (CNS) is hindered by poor blood-brain barrier (BBB) penetration and the invasiveness of intrathecal administration. In the current study, we demonstrate effective systemic delivery of a next-generation SOD1 ASO (Tofersen) into the brain of wildtype and G93A-SOD1 transgenic C57BL/6 mice using calcium phosphate lipid nanoparticles (CaP lipid NPs). We show that transcranial focused ultrasound (FUS) with intravenously administered microbubbles can significantly enhance ASO-loaded nanoparticle delivery into the mouse brain. Magnetic resonance imaging (MRI) and immunohistological analysis showed reduced SOD1 expression in the FUS-exposed brain regions and increased motor neuron count in the spinal cord of treated mice suggesting decreased motor neuron degeneration. Importantly, the BBB opening was transient without evidence of structural changes, neuroinflammation or damage to the brain tissue, indicating that the treatment is well tolerated. Overall, our results highlight FUS-assisted nanoparticle delivery of ASOs as a promising non-invasive therapeutic strategy for the treatment of ALS and CNS diseases more broadly.

Focused Ultrasound for Neurodegenerative Diseases

Neurodegenerative diseases are a leading cause of death and disability and pose a looming global public health crisis. Despite progress in understanding biological and molecular factors associated with these disorders and their progression, effective disease modifying treatments are presently limited. Focused ultrasound (FUS) is an emerging therapeutic strategy for Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. In these contexts, applications of FUS include neuroablation, neuromodulation, and/or blood-brain barrier opening with and without facilitated intracerebral drug delivery. Here, the authors review preclinical evidence and current and emerging applications of FUS for neurodegenerative diseases and summarize future directions in the field.

A patient-derived amyotrophic lateral sclerosis blood-brain barrier model for focused ultrasound-mediated anti-TDP-43 antibody delivery

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a rapidly progressing neurodegenerative disorder with minimally effective treatment options. An important hurdle in ALS drug development is the non-invasive therapeutic access to the motor cortex currently limited by the presence of the blood-brain barrier (BBB). Focused ultrasound and microbubble (FUS+ MB) treatment is an emerging technology that was successfully used in ALS patients to temporarily open the cortical BBB. However, FUS+ MB-mediated drug delivery across ALS patients' BBB has not yet been reported. Similarly, the effects of FUS+ MB on human ALS BBB cells remain unexplored.

METHODS

Here we established the first FUS+ MB-compatible, fully-human ALS patient-cell-derived BBB model based on induced brain endothelial-like cells (iBECs) to study anti-TDP-43 antibody delivery and FUS+ MB bioeffects in vitro.

RESULTS

Generated ALS iBECs recapitulated disease-specific hallmarks of BBB pathology, including reduced BBB integrity and permeability, and TDP-43 proteinopathy. The results also identified differences between sporadic ALS and familial (C9orf72 expansion carrying) ALS iBECs reflecting patient heterogeneity associated with disease subgroups. Studies in these models revealed successful ALS iBEC monolayer opening in vitro with no adverse cellular effects of FUS+ MB as reflected by lactate dehydrogenase (LDH) release viability assay and the lack of visible monolayer damage or morphology change in FUS+ MB treated cells. This was accompanied by the molecular bioeffects of FUS+ MB in ALS iBECs including changes in expression of tight and adherens junction markers, and drug transporter and inflammatory mediators, with sporadic and C9orf72 ALS iBECs generating transient specific responses. Additionally, we demonstrated an effective increase in the delivery of anti-TDP-43 antibody with FUS+ MB in C9orf72 (2.7-fold) and sporadic (1.9-fold) ALS iBECs providing the first proof-of-concept evidence that FUS+ MB can be used to enhance the permeability of large molecule therapeutics across the BBB in a human ALS in vitro model.

CONCLUSIONS

Together, this study describes the first characterisation of cellular and molecular responses of ALS iBECs to FUS+ MB and provides a fully-human platform for FUS+ MB-mediated drug delivery screening on an ALS BBB in vitro model.

Recent advances of focused ultrasound induced blood-brain barrier opening for clinical applications of neurodegenerative diseases

With the aging population on the rise, neurodegenerative disorders have taken center stage as a significant health concern. The blood-brain barrier (BBB) plays an important role to maintain the stability of central nervous system, yet it poses a formidable obstacle to delivering drugs for neurodegenerative disease therapy. Various methods have been devised to confront this challenge, each carrying its own set of limitations. One particularly promising noninvasive approach involves the utilization of focused ultrasound (FUS) combined with contrast agents-microbubbles (MBs) to achieve transient and reversible BBB opening. This review provides a comprehensive exploration of the fundamental mechanisms behind FUS/MBs-mediated BBB opening and spotlights recent breakthroughs in its application for neurodegenerative diseases. Furthermore, it addresses the current challenges and presents future perspectives in this field.

Multimodal evaluation of blood-brain barrier opening in mice in response to low-intensity ultrasound and a claudin-5 binder

Background: The blood-brain barrier (BBB) is a major bottleneck in delivering therapeutics to the brain. Treatment strategies to transiently open this barrier include focused ultrasound combined with intravenously injected microbubbles (FUS+MB) and targeting of molecules that regulate BBB permeability. Methods: Here, we investigated BBB opening mediated by the claudin-5 binder cCPEm (a microorganismal toxin in a truncated form) and FUS+MB at a centre frequency of 1 MHz, assessing dextran uptake, broadband emission, and endogenous immunoglobulin G (IgG) extravasation. Results: FUS+MB-induced BBB opening was detectable at a pressure ≥0.35 MPa when assessed for leakage of 10 and 70 kDa dextran, and at ≥0.2 MPa for uptake of endogenous IgG. Treating mice with 20 mg/kg cCPEm failed to open the BBB, and pre-treatment with cCPEm followed by FUS+MB at 0.2 and 0.3 MPa did not overtly increase BBB opening compared to FUS+MB alone. Using passive cavitation detection (PCD), we found that broadband emission correlated with the peak negative pressure (PNP) and dextran leakage, indicating the possibility of using broadband emission for developing a feedback controller to monitor BBB opening. Conclusions: Together, our study highlights the challenges in developing combinatorial approaches to open the BBB and presents an additional IgG-based histological detection method for BBB opening.

Current clinical investigations of focused ultrasound blood-brain barrier disruption: A review

The blood-brain barrier (BBB) presents a formidable challenge in delivering therapeutic agents to the central nervous system. Ultrasound-mediated BBB disruption has emerged as a promising non-invasive technique to enhance drug delivery to the brain. This manuscript reviews fundamental principles of ultrasound-based techniques and their mechanisms of action in temporarily permeabilizing the BBB. Clinical trials employing ultrasound for BBB disruption are discussed, summarizing diverse applications ranging from the treatment of neurodegenerative diseases to targeted drug delivery for brain tumors. The review also addresses safety considerations, outlining the current understanding of potential risks and mitigation strategies associated with ultrasound exposure, including real-time monitoring and assessment of treatment efficacy. Among the large number of studies, significant successes are highlighted thus providing perspective on the future direction of the field.

Focused ultrasound-assisted delivery of immunomodulating agents in brain cancer

Focused ultrasound (FUS) combined with intravascularly circulating microbubbles can transiently increase the permeability of the blood-brain barrier (BBB) to enable targeted therapeutic delivery to the brain, the clinical testing of which is currently underway in both adult and pediatric patients. Aside from traditional cancer drugs, this technique is being extended to promote the delivery of immunomodulating therapeutics to the brain, including antibodies, immune cells, and cytokines. In this manner, FUS approaches are being explored as a tool to improve and amplify the effectiveness of immunotherapy for both primary and metastatic brain cancer, a particularly challenging solid tumor to treat. Here, we present an overview of the latest groundbreaking research in FUS-assisted delivery of immunomodulating agents to the brain in pre-clinical models of brain cancer, and place it within the context of the current immunotherapy approaches. We follow this up with a discussion on new developments and emerging strategies for this rapidly evolving approach.

A multicellular brain spheroid model for studying the mechanisms and bioeffects of ultrasound-enhanced drug penetration beyond the blood‒brain barrier

The blood‒brain barrier (BBB) acts as a hindrance to drug therapy reaching the brain. With an increasing incidence of neurovascular diseases and brain cancer metastases, there is a need for an ideal in vitro model to develop novel methodologies for enhancing drug delivery to the brain. Here, we established a multicellular human brain spheroid model that mimics the BBB both architecturally and functionally. Within the spheroids, endothelial cells and pericytes localized to the periphery, while neurons, astrocytes, and microglia were distributed throughout. Ultrasound-targeted microbubble cavitation (UTMC) is a novel noninvasive technology for enhancing endothelial drug permeability. We utilized our three-dimensional (3D) model to study the feasibility and mechanisms regulating UTMC-induced hyperpermeability. UTMC caused a significant increase in the penetration of 10 kDa Texas red dextran (TRD) into the spheroids, 100 µm beyond the BBB, without compromising cell viability. This hyperpermeability was dependent on UTMC-induced calcium (Ca2+) influx and endothelial nitric oxide synthase (eNOS) activation. Our 3D brain spheroid model, with its intact and functional BBB, offers a valuable platform for studying the bioeffects of UTMC, including effects occurring spatially distant from the endothelial barrier.

Receptor-mediated drug delivery of bispecific therapeutic antibodies through the blood-brain barrier

Therapeutic antibody drug development is a rapidly growing sector of the pharmaceutical industry. However, antibody drug development for the brain is a technical challenge, and therapeutic antibodies for the central nervous system account for ~3% of all such agents. The principal obstacle to antibody drug development for brain or spinal cord is the lack of transport of large molecule biologics across the blood-brain barrier (BBB). Therapeutic antibodies can be made transportable through the blood-brain barrier by the re-engineering of the therapeutic antibody as a BBB-penetrating bispecific antibody (BSA). One arm of the BSA is the therapeutic antibody and the other arm of the BSA is a transporting antibody. The transporting antibody targets an exofacial epitope on a BBB receptor, and this enables receptor-mediated transcytosis (RMT) of the BSA across the BBB. Following BBB transport, the therapeutic antibody then engages the target receptor in brain. RMT systems at the BBB that are potential conduits to the brain include the insulin receptor (IR), the transferrin receptor (TfR), the insulin-like growth factor receptor (IGFR) and the leptin receptor. Therapeutic antibodies have been re-engineered as BSAs that target the insulin receptor, TfR, or IGFR RMT systems at the BBB for the treatment of Alzheimer's disease and Parkinson's disease.

Targeting cerebral diseases with enhanced delivery of therapeutic proteins across the blood-brain barrier

INTRODUCTION

Cerebral diseases have been threatening public physical and psychological health in the recent years. With the existence of the blood-brain barrier (BBB), it is particularly hard for therapeutic proteins like peptides, enzymes, antibodies, etc. to enter the central nervous system (CNS) and function in diagnosis and treatment in cerebral diseases. Fortunately, the past decade has witnessed some emerging strategies of delivering macromolecular therapeutic proteins across the BBB.

AREAS COVERED

Based on the structure, functions, and substances transport mechanisms, various enhanced delivery strategies of therapeutic proteins were reviewed, categorized by molecule-mediated delivery strategies, carrier-mediated delivery strategies, and other delivery strategies.

EXPERT OPINION

As for molecule-mediated delivery strategies, development of genetic engineering technology, optimization of protein expression and purification techniques, and mature of quality control systems all help to realize large-scale production of recombinant antibodies, making it possible to apply to the clinical practice. In terms of carrier-mediated delivery strategies and others, although nano-carriers/adeno-associated virus (AAV) are also promising candidates for delivering therapeutic proteins or genes across the BBB, some issues still remain to be further investigated, including safety concerns related to applied materials, large-scale production costs, quality control standards, combination therapies with auxiliary delivery strategies like focused ultrasound, etc.

Alzheimer's Disease: Significant Benefit from the Yeast-Based Models

Alzheimer's disease (AD) is an age-related, multifaceted neurological disorder associated with accumulation of aggregated proteins (amyloid Aβ and hyperphosphorylated tau), loss of synapses and neurons, and alterations in microglia. AD was recognized by the World Health Organization as a global public health priority. The pursuit of a better understanding of AD forced researchers to pay attention to well-defined single-celled yeasts. Yeasts, despite obvious limitations in application to neuroscience, show high preservation of basic biological processes with all eukaryotic organisms and offer great advantages over other disease models due to the simplicity, high growth rates on low-cost substrates, relatively simple genetic manipulations, the large knowledge base and data collections, and availability of an unprecedented amount of genomic and proteomic toolboxes and high-throughput screening techniques, inaccessible to higher organisms. Research reviewed above clearly indicates that yeast models, together with other, more simple eukaryotic models including animal models, C. elegans and Drosophila, significantly contributed to understanding Aβ and tau biology. These models allowed high throughput screening of factors and drugs that interfere with Aβ oligomerization, aggregation and toxicity, and tau hyperphosphorylation. In the future, yeast models will remain relevant, with a focus on creating novel high throughput systems to facilitate the identification of the earliest AD biomarkers among different cellular networks in order to achieve the main goal-to develop new promising therapeutic strategies to treat or prevent the disease.

Access to the CNS: Strategies to overcome the BBB

The blood-brain barrier (BBB) limits the access of substances to the central nervous system (CNS) which hinders the treatment of pathologies affecting the brain and the spinal cord. Nowadays, research is focus on new strategies to overcome the BBB and can treat the pathologies affecting the CNS are needed. In this review, the different strategies that allow and increase the access of substances to the CNS are analysed and extended commented, not only invasive strategies but also non-invasive ones. The invasive techniques include the direct injection into the brain parenchyma or the CSF and the therapeutic opening of the BBB, while the non-invasive techniques include the use of alternative routes of administration (nose-to-brain route), the inhibition of efflux transporters (as it is important to prevent the drug efflux from the brain and enhance the therapeutic efficiency), the chemical modification of the molecules (prodrugs and chemical drug delivery systems (CDDS)) and the use of nanocarriers. In the future, knowledge about nanocarriers to treat CNS diseases will continue to increase, but the use of other strategies such as drug repurposing or drug reprofiling, which are cheaper and less time consuming, may limit its transfer to society. The main conclusion is that the combination of different strategies may be the most interesting approach to increase the access of substances to the CNS.

Altered Mitochondrial Morphology and Bioenergetics in a New Yeast Model Expressing Aβ42

Alzheimer's disease (AD) is an incurable, age-related neurological disorder, the most common form of dementia. Considering that AD is a multifactorial complex disease, simplified experimental models are required for its analysis. For this purpose, genetically modified Yarrowia lipolytica yeast strains expressing Aβ42 (the main biomarker of AD), eGFP-Aβ42, Aβ40, and eGFP-Aβ40 were constructed and examined. In contrast to the cells expressing eGFP and eGFP-Aβ40, retaining "normal" mitochondrial reticulum, eGFP-Aβ42 cells possessed a disturbed mitochondrial reticulum with fragmented mitochondria; this was partially restored by preincubation with a mitochondria-targeted antioxidant SkQThy. Aβ42 expression also elevated ROS production and cell death; low concentrations of SkQThy mitigated these effects. Aβ42 expression caused mitochondrial dysfunction as inferred from a loose coupling of respiration and phosphorylation, the decreased level of ATP production, and the enhanced rate of hydrogen peroxide formation. Therefore, we have obtained the same results described for other AD models. Based on an analysis of these and earlier data, we suggest that the mitochondrial fragmentation might be a biomarker of the earliest preclinical stage of AD with an effective therapy based on mitochondria- targeted antioxidants. The simple yeast model constructed can be a useful platform for the rapid screening of such compounds.

Reconsidering the role of blood-brain barrier in Alzheimer's disease: From delivery to target

The existence of a selective blood-brain barrier (BBB) and neurovascular coupling are two unique central nervous system vasculature features that result in an intimate relationship between neurons, glia, and blood vessels. This leads to a significant pathophysiological overlap between neurodegenerative and cerebrovascular diseases. Alzheimer's disease (AD) is the most prevalent neurodegenerative disease whose pathogenesis is still to be unveiled but has mostly been explored under the light of the amyloid-cascade hypothesis. Either as a trigger, bystander, or consequence of neurodegeneration, vascular dysfunction is an early component of the pathological conundrum of AD. The anatomical and functional substrate of this neurovascular degeneration is the BBB, a dynamic and semi-permeable interface between blood and the central nervous system that has consistently been shown to be defective. Several molecular and genetic changes have been demonstrated to mediate vascular dysfunction and BBB disruption in AD. The isoform ε4 of Apolipoprotein E is at the same time the strongest genetic risk factor for AD and a known promoter of BBB dysfunction. Low-density lipoprotein receptor-related protein 1 (LRP-1), P-glycoprotein, and receptor for advanced glycation end products (RAGE) are examples of BBB transporters implicated in its pathogenesis due to their role in the trafficking of amyloid-β. This disease is currently devoid of strategies that change the natural course of this burdening illness. This unsuccess may partly be explained by our misunderstanding of the disease pathogenesis and our inability to develop drugs that are effectively delivered to the brain. BBB may represent a therapeutic opportunity as a target itself or as a therapeutic vehicle. In this review, we aim to explore the role of BBB in the pathogenesis of AD including the genetic background and detail how it can be targeted in future therapeutic research.

Disease-Modifying Effects of Non-Invasive Electroceuticals on β-Amyloid Plaques and Tau Tangles for Alzheimer's Disease

Electroceuticals refer to various forms of electronic neurostimulators used for therapy. Interdisciplinary advances in medical engineering and science have led to the development of the electroceutical approach, which involves therapeutic agents that specifically target neural circuits, to realize precision therapy for Alzheimer's disease (AD). To date, extensive studies have attempted to elucidate the disease-modifying effects of electroceuticals on areas in the brain of a patient with AD by the use of various physical stimuli, including electric, magnetic, and electromagnetic waves as well as ultrasound. Herein, we review non-invasive stimulatory systems and their effects on β-amyloid plaques and tau tangles, which are pathological molecular markers of AD. Therefore, this review will aid in better understanding the recent technological developments, applicable methods, and therapeutic effects of electronic stimulatory systems, including transcranial direct current stimulation, 40-Hz gamma oscillations, transcranial magnetic stimulation, electromagnetic field stimulation, infrared light stimulation and ionizing radiation therapy, and focused ultrasound for AD.

Applications of focused ultrasound-mediated blood-brain barrier opening

The blood brain barrier (BBB) plays a critically important role in the regulation of central nervous system (CNS) homeostasis, but also represents a major limitation to treatments of brain pathologies. In recent years, focused ultrasound (FUS) in conjunction with gas-filled microbubble contrast agents has emerged as a powerful tool for transiently and non-invasively disrupting the BBB in a targeted and image-guided manner, allowing for localized delivery of drugs, genes, or other therapeutic agents. Beyond the delivery of known therapeutics, FUS-mediated BBB opening also demonstrates the potential for use in neuromodulation and the stimulation of a range of cell- and tissue-level physiological responses that may prove beneficial in disease contexts. Clinical trials investigating the safety and efficacy of FUS-mediated BBB opening are well underway, and offer promising non-surgical approaches to treatment of devastating pathologies. This article reviews a range of pre-clinical and clinical studies demonstrating the tremendous potential of FUS to fundamentally change the paradigm of treatment for CNS diseases.

Ultrasound-mediated blood-brain barrier opening: An effective drug delivery system for theranostics of brain diseases

Blood-brain barrier (BBB) remains a significant obstacle to drug therapy for brain diseases. Focused ultrasound (FUS) combined with microbubbles (MBs) can locally and transiently open the BBB, providing a potential strategy for drug delivery across the BBB into the brain. Nowadays, taking advantage of this technology, many therapeutic agents, such as antibodies, growth factors, and nanomedicine formulations, are intensively investigated across the BBB into specific brain regions for the treatment of various brain diseases. Several preliminary clinical trials also have demonstrated its safety and good tolerance in patients. This review gives an overview of the basic mechanisms, ultrasound contrast agents, evaluation or monitoring methods, and medical applications of FUS-mediated BBB opening in glioblastoma, Alzheimer's disease, and Parkinson's disease.

Opportunities and challenges in delivering biologics for Alzheimer's disease by low-intensity ultrasound

Low-intensity ultrasound combined with intravenously injected microbubbles (US^+MB) is a novel treatment modality for brain disorders, including Alzheimer's disease (AD), safely and transiently allowing therapeutic agents to overcome the blood-brain barrier (BBB) that constitutes a major barrier for therapeutic agents. Here, we first provide an update on immunotherapies in AD and how US^+MB has been applied to AD mouse models and in clinical trials, considering the ultrasound and microbubble parameter space. In the second half of the review, we compare different in vitro BBB models and discuss strategies for combining US^+MB with BBB modulators (targeting molecules such as claudin-5), and highlight the insight provided by super-resolution microscopy. Finally, we conclude with a short discussion on how in vitro findings can inform the design of animal studies, and how the insight gained may aid treatment optimization in the clinical ultrasound space.

Enhanced delivery to brain using sonosensitive liposome and microbubble with focused ultrasound

Glioblastoma is considered one of the most aggressive and dangerous brain tumors. However, treatment of GBM has been still challenged due to blood-brain barrier (BBB). BBB prevents that the chemotherapeutic molecules are extravasated to brain. In this study, sonosensitive liposome encapsulating doxorubicin (DOX) was developed for enhancement of GBM penetration in combination with focused ultrasound (FUS) and microbubbles. Upon ultrasound (US) irradiation, microbubbles induce cavitation resulting in the tight junction of BBB endothelium to temporarily open. In addition, the composition of sonosensitive liposome was optimized by comparison of sonosensitivity and intracellular uptake to U87MG cells. The optimal sonosensitive liposome, IMP301-DC, resulted 123.9 ± 38.2 nm in size distribution and 98.2 % in loading efficiency. Related to sonosensitivity of IMP301-DC, US-triggered release ratio of doxorubicin was 69.2 ± 12.3 % at 92 W/cm² of US intensity for 1 min. In the in vivo experiments, the accumulation of DiD fluorescence probe labeled IMP301-DC-shell in the brain through the BBB opening was increased more than two-fold compared to that of Doxil-shell, non-sonosensitive liposome. US exposure significantly increased GBM cytotoxicity of IMP301-DC. In conclusion, this study demonstrated that IMP301-DC could serve as an alternative solution to enhance the penetration to GBM treatment via BBB opening by non-invasive FUS combined with microbubbles.

Functionalization strategies of polymeric nanoparticles for drug delivery in Alzheimer's disease: Current trends and future perspectives

Alzheimer's disease (AD), the most common form of dementia, is a progressive and multifactorial neurodegenerative disorder whose primary causes are mostly unknown. Due to the increase in life expectancy of world population, including developing countries, AD, whose incidence rises dramatically with age, is at the forefront among neurodegenerative diseases. Moreover, a definitive cure is not yet within reach, imposing substantial medical and public health burdens at every latitude. Therefore, the effort to devise novel and effective therapeutic strategies is still of paramount importance. Genetic, functional, structural and biochemical studies all indicate that new and efficacious drug delivery strategies interfere at different levels with various cellular and molecular targets. Over the last few decades, therapeutic development of nanomedicine at preclinical stage has shown to progress at a fast pace, thus paving the way for its potential impact on human health in improving prevention, diagnosis, and treatment of age-related neurodegenerative disorders, including AD. Clinical translation of nano-based therapeutics, despite current limitations, may present important advantages and innovation to be exploited in the neuroscience field as well. In this state-of-the-art review article, we present the most promising applications of polymeric nanoparticle-mediated drug delivery for bypassing the blood-brain barrier of AD preclinical models and boost pharmacological safety and efficacy. In particular, novel strategic chemical functionalization of polymeric nanocarriers that could be successfully employed for treating AD are thoroughly described. Emphasis is also placed on nanotheranostics as both potential therapeutic and diagnostic tool for targeted treatments. Our review highlights the emerging role of nanomedicine in the management of AD, providing the readers with an overview of the nanostrategies currently available to develop future therapeutic applications against this chronic neurodegenerative disease.

Ultrasound-mediated delivery of novel tau-specific monoclonal antibody enhances brain uptake but not therapeutic efficacy

Tau-specific immunotherapy is an attractive strategy for the treatment of Alzheimer's disease and other tauopathies. However, effectively targeting tau in the brain remains a considerable challenge due to the restrictive nature of the blood-brain barrier (BBB), which excludes an estimated >99% of peripherally administered antibodies. However, their transport across the BBB can be facilitated by a novel modality, low-intensity scanning ultrasound used in combination with intravenously injected microbubbles (SUS^+MB). We have previously shown that SUS^+MB-mediated delivery of a tau-specific antibody in a single-chain (scFv) format to tau transgenic mice enhanced brain and neuronal uptake and subsequently, reduced tau pathology and improved behavioural outcomes to a larger extent than either scFv or SUS^+MB on its own. Here we generated a novel tau-specific monoclonal antibody, RNF5, and validated it in its IgG format in the presence or absence of SUS^+MB by treating K369I tau transgenic K3 mice once weekly for 12 weeks. We found that both RNF5 and SUS^+MB treatments on their own significantly reduced tau pathology. In the combination group (RNF5 + SUS^+MB), however, despite increased antibody localization in the brain, there were no further reductions in tau pathology when compared to RNF5 treatment alone. Furthermore, following SUS^+MB, RNF5 accumulated heavily within cells across the pyramidal cell layer of the hippocampus, that were negative for MAP2 and p-tau, suggesting that SUS^+MB may not facilitate enhanced RNF5 engagement of intraneuronal tau. Overall, our new findings reveal the complexities of combining tau immunotherapy with SUS^+MB and challenge the view that this is a straight-forward approach.

Ultrasound-Mediated Bioeffects in Senescent Mice and Alzheimer's Mouse Models

Ultrasound is routinely used for a wide range of diagnostic imaging applications. However, given that ultrasound can operate over a wide range of parameters that can all be modulated, its applicability extends far beyond the bioimaging field. In fact, the modality has emerged as a hybrid technology that effectively assists drug delivery by transiently opening the blood-brain barrier (BBB) when combined with intravenously injected microbubbles, and facilitates neuromodulation. Studies in aged mice contributed to an insight into how low-intensity ultrasound brings about its neuromodulatory effects, including increased synaptic plasticity and improved cognitive functions, with a potential role for neurogenesis and the modulation of NMDA receptor-mediated neuronal signalling. This work is complemented by studies in mouse models of Alzheimer's disease (AD), a form of pathological ageing. Here, ultrasound was mainly employed as a BBB-opening tool that clears protein aggregates via microglial activation and neuronal autophagy, thereby restoring cognition. We discuss the currently available ultrasound approaches and how studies in senescent mice are relevant for AD and can accelerate the application of low-intensity ultrasound in the clinic.

Exploiting Focused Ultrasound to Aid Intranasal Drug Delivery for Brain Therapy

Novel effective therapeutic strategies are needed to treat brain neurodegenerative diseases and to improve the quality of life of patients affected by Alzheimer’s disease (AD), Parkinson’s disease (PD), Huntington’s disease (HD), Amyotrophic Lateral sclerosis (ALS) as well as other brain conditions. At present no effective treatment options are available; current therapeutics for neurodegenerative diseases (NDs) improve cognitive symptoms only transiently and in a minor number of patients. Further, most of the amyloid-based phase III clinical trials recently failed in AD, in spite of promising preclinical and phase I-II clinical trials, further pinpointing the need for a better knowledge of the early mechanisms of disease as well as of more effective routes of drug administration. In fact, beyond common pathological events and molecular substrates, each of these diseases preferentially affect defined subpopulations of neurons in specific neuronal circuits (selective neuronal vulnerability), leading to the typical age-related clinical profile. In this perspective, key to successful drug discovery is a robust and reproducible biological validation of potential new molecular targets together with a concomitant set up of protocols/tools for efficient and targeted brain delivery to a specific area of interest. Here we propose and discuss Focused UltraSound aided drug administration as a specific and novel technical approach to achieve optimal concentration of the drug at the target area of interest. We will focus on drug delivery to the brain through the nasal route coupled to FUS as a promising approach to achieve neuroprotection and rescue of cognitive decline in several NDs.

Translation of focused ultrasound for blood-brain barrier opening in glioma

Survival outcomes for patients with glioblastoma multiforme (GBM) have remained poor for the past 15 years, reflecting a clear challenge in the development of more effective treatment strategies. The efficacy of systemic therapies for GBM is greatly limited by the presence of the blood-brain barrier (BBB), which prevents drug penetration and accumulation in regions of infiltrative tumour, as represented in a consistent portion of GBM lesions. Focused ultrasound (FUS) - a technique that uses low-frequency ultrasound waves to induce targeted temporary disruption of the BBB - promises to improve survival outcomes by enhancing drug delivery and accumulation to infiltrating tumour regions. In this review we discuss the current state of preclinical investigations using FUS to enhance delivery of systemic therapies to intracranial neoplasms. We highlight critical methodological inconsistencies that are hampering clinical translation of FUS and we provide guiding principles for future preclinical studies. Particularly, we focus our attention on the importance of the selection of clinically relevant animal models and to the standardization of methods for FUS delivery, which will be paramount to the successful clinical translation of this promising technology for treatment in GBM patients. We also discuss how preclinical FUS research can benefit the development of GBM immunotherapies.

"Focused Ultrasound-mediated Drug Delivery in Humans - a Path Towards Translation in Neurodegenerative Diseases"

The blood-brain barrier (BBB) has a major protective function in preventing the entry of harmful molecules into the brain, but is simultaneously limiting the delivery of drugs, restricting their potential clinical application in neurodegenerative diseases. Recent preclinical evidence demonstrates that following application of focused ultrasound with microbubbles (FUS+MB), the BBB becomes reversibly accessible to compounds that normally are brain-impermeable, suggesting FUS+MB as a promising new platform for delivery of therapeutic agents into the central nervous system. As a step towards translation, small cohort clinical studies were performed demonstrating safe BBB opening in Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis (ALS) patients following FUS+MB, however improved drug delivery has not yet been achieved in human. Simultaneously, rapid progress in the human induced pluripotent stem cell (hiPSC) modeling technology allowed for development of novel Alzheimer's disease patient-derived BBB in vitro model that reacts to FUS+MB with BBB opening and can be used to answer fundamental questions of human BBB responses to FUS+MB in health and disease. This review summarizes key features of the BBB that contribute to limited drug delivery, recapitulates recent advances in the FUS+MB mediated human BBB opening in vivo and in vitro in the context of neurodegenerative disorders, and highlights potential strategies for fast-track translation of the FUS+MB to improve bioavailability of drugs to the human brain. With safe and effective application, this innovative FUS+MB technology may open new avenues for therapeutic interventions in neurodegenerative diseases leading to improved clinical outcomes for patients.

Noninvasive Delivery of Biologicals to the Brain

In the past, psychotherapy and neuropharmacological approaches have been the most common treatments for disordered thoughts, moods, and behaviors. One new path of brain therapeutics is in the deployment of noninvasive approaches designed to reprogram brain function at the cellular level. Treatment at the cellular level may be considered for a wide array of disorders, ranging from mood disorders to neurodegenerative disorders. Brain-targeted biological therapy may provide minimally invasive and accurate delivery of treatment. The present article discusses the hurdles and advances that characterize the pathway to this goal.

The Applications of Focused Ultrasound (FUS) in Alzheimer's Disease Treatment: A Systematic Review on Both Animal and Human Studies

Alzheimer's disease (AD) affects the basic ability to function and has imposed an immense burden on the community and health care system. Focused ultrasound (FUS) has recently been proposed as a novel noninvasive therapeutic approach for AD. However, systematic reviews on the FUS application in AD treatment have not been forthcoming. We followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) criteria to summarize the techniques associated with safety and efficacy, as well as possible underlying mechanisms of FUS effects on AD in animal and human studies. Animal studies demonstrated FUS with microbubbles (FUS-MB) induced blood-brain-barrier (BBB) opening that could facilitate various therapeutic agents entering the brain. Repeated FUS-MB and FUS stimulation can relieve AD pathology and improve cognitive and memory function. Human studies showed repeated FUS-MB are well tolerated with few adverse events and FUS stimulation could enhance local perfusion and neural function, which correlated with cognitive improvement. We conclude that FUS is a feasible and safe therapeutic and drug delivery strategy for AD. However, FUS treatment on humans is still in the early stages and requires further optimization and standardization.

Current and Emerging Strategies for Enhancing Antibody Delivery to the Brain

For the treatment of neurological diseases, achieving sufficient exposure to the brain parenchyma is a critical determinant of drug efficacy. The blood-brain barrier (BBB) functions to tightly control the passage of substances between the bloodstream and the central nervous system, and as such poses a major obstacle that must be overcome for therapeutics to enter the brain. Monoclonal antibodies have emerged as one of the best-selling treatment modalities available in the pharmaceutical market owing to their high target specificity. However, it has been estimated that only 0.1% of peripherally administered antibodies can cross the BBB, contributing to the low success rate of immunotherapy seen in clinical trials for the treatment of neurological diseases. The development of new strategies for antibody delivery across the BBB is thereby crucial to improve immunotherapeutic efficacy. Here, we discuss the current strategies that have been employed to enhance antibody delivery across the BBB. These include (i) focused ultrasound in combination with microbubbles, (ii) engineered bi-specific antibodies, and (iii) nanoparticles. Furthermore, we discuss emerging strategies such as extracellular vesicles with BBB-crossing properties and vectored antibody genes capable of being encapsulated within a BBB delivery vehicle.

Multiple regression analysis of a comprehensive transcriptomic data assembly elucidates mechanically- and biochemically-driven responses to focused ultrasound blood-brain barrier disruption

Background: Focused ultrasound (FUS) blood brain barrier disruption (BBBD) permits the noninvasive, targeted, and repeatable delivery of drugs to the brain. FUS BBBD also elicits secondary responses capable of augmenting immunotherapies, clearing amyloid-β and hyperphosphorylated tau, and driving neurogenesis. Leveraging these secondary effects will benefit from an understanding of how they correlate to the magnitude of FUS BBBD and are differentially affected by the mechanical and biochemical stimuli imparted during FUS BBBD.

Methods: We aggregated 75 murine transcriptomes in a multiple regression framework to identify genes expressed in proportion to biochemical (i.e. contrast MR image enhancement (CE)) or mechanical (i.e. harmonic acoustic emissions from MB-activation (MBA)) stimuli associated with FUS BBBD. Models were constructed to control for potential confounders, such as sex, anesthesia, and sequencing batch.

Results: MBA and CE differentially predicted expression of 1,124 genes 6 h or 24 h later. While there existed overlap in the transcripts correlated with MBA vs CE, MBA was principally predictive of expression of genes associated with endothelial reactivity while CE chiefly predicted sterile inflammation gene sets. Over-representation analysis identified transcripts not previously linked to BBBD, including actin filament organization, which is likely important for BBB recovery. Transcripts and pathways associated with neurogenesis, microglial activation, and amyloid-β clearance were significantly correlated to BBBD metrics.

Conclusions: The secondary effects of BBBD may have the potential to be tuned by modulating FUS parameters during BBBD, and MBA and CE may serve as independent predictors of transcriptional reactions in the brain.

Therapeutic antibodies - natural and pathological barriers and strategies to overcome them

Antibody-based therapeutics have become a major class of therapeutics with over 120 recombinant antibodies approved or under review in the EU or US. This therapeutic class has experienced a remarkable expansion with an expected acceleration in 2021-2022 due to the extraordinary global response to SARS-CoV2 pandemic and the public disclosure of over a hundred anti-SARS-CoV2 antibodies. Mainly delivered intravenously, alternative delivery routes have emerged to improve antibody therapeutic index and patient comfort. A major hurdle for antibody delivery and efficacy as well as the development of alternative administration routes, is to understand the different natural and pathological barriers that antibodies face as soon as they enter the body up to the moment they bind to their target antigen. In this review, we discuss the well-known and more under-investigated extracellular and cellular barriers faced by antibodies. We also discuss some of the strategies developed in the recent years to overcome these barriers and increase antibody delivery to its site of action. A better understanding of the biological barriers that antibodies have to face will allow the optimization of antibody delivery near its target. This opens the way to the development of improved therapy with less systemic side effects and increased patients' adherence to the treatment.

Multi-mechanical waves against Alzheimer's disease pathology: a systematic review

Alzheimer’s disease (AD) is the most common cause of dementia, affecting approximately 40 million people worldwide. The ineffectiveness of the available pharmacological treatments against AD has fostered researchers to focus on alternative strategies to overcome this challenge. Mechanical vibrations delivered in different stimulation modes have been associated with marked improvements in cognitive and physical performance in both demented and non-demented elderly. Some of the mechanical-based stimulation modalities in efforts are earlier whole-body vibration, transcranial ultrasound stimulation with microbubble injection, and more recently, auditory stimulation. However, there is a huge variety of treatment specifications, and in many cases, conflicting results are reported. In this review, a search on Scopus, PubMed, and Web of Science databases was performed, resulting in 37 papers . These studies suggest that mechanical vibrations delivered through different stimulation modes are effective in attenuating many parameters of AD pathology including functional connectivity and neuronal circuit integrity deficits in the brains of AD patients, as well as in subjects with cognitive decline and non-demented older adults. Despite the evolving preclinical and clinical evidence on these therapeutic modalities, their translation into clinical practice is not consolidated yet. Thus, this comprehensive and critical systematic review aims to address the most important gaps in the reviewed protocols and propose optimal regimens for future clinical application.

Development of Novel Therapeutics Targeting the Blood-Brain Barrier: From Barrier to Carrier

The blood-brain barrier (BBB) is a highly specialized neurovascular unit, initially described as an intact barrier to prevent toxins, pathogens, and potentially harmful substances from entering the brain. An intact BBB is also critical for the maintenance of normal neuronal function. In cerebral vascular diseases and neurological disorders, the BBB can be disrupted, contributing to disease progression. While restoration of BBB integrity serves as a robust biomarker of better clinical outcomes, the restrictive nature of the intact BBB presents a major hurdle for delivery of therapeutics into the brain. Recent studies show that the BBB is actively engaged in crosstalk between neuronal and the circulatory systems, which defines another important role of the BBB: as an interfacing conduit that mediates communication between two sides of the BBB. This role has been subject to extensive investigation for brain-targeted drug delivery and shows promising results. The dual roles of the BBB make it a unique target for drug development. Here, recent developments and novel strategies to target the BBB for therapeutic purposes are reviewed, from both barrier and carrier perspectives.

Transportation of Single-Domain Antibodies through the Blood-Brain Barrier

Single-domain antibodies derive from the heavy-chain-only antibodies of Camelidae (camel, dromedary, llama, alpaca, vicuñas, and guananos; i.e., nanobodies) and cartilaginous fishes (i.e., VNARs). Their small size, antigen specificity, plasticity, and potential to recognize unique conformational epitopes represent a diagnostic and therapeutic opportunity for many central nervous system (CNS) pathologies. However, the blood–brain barrier (BBB) poses a challenge for their delivery into the brain parenchyma. Nevertheless, numerous neurological diseases and brain pathologies, including cancer, result in BBB leakiness favoring single-domain antibodies uptake into the CNS. Some single-domain antibodies have been reported to naturally cross the BBB. In addition, different strategies and methods to deliver both nanobodies and VNARs into the brain parenchyma can be exploited when the BBB is intact. These include device-based and physicochemical disruption of the BBB, receptor and adsorptive-mediated transcytosis, somatic gene transfer, and the use of carriers/shuttles such as cell-penetrating peptides, liposomes, extracellular vesicles, and nanoparticles. Approaches based on single-domain antibodies are reaching the clinic for other diseases. Several tailoring methods can be followed to favor the transport of nanobodies and VNARs to the CNS, avoiding the limitations imposed by the BBB to fulfill their therapeutic, diagnostic, and theragnostic promises for the benefit of patients suffering from CNS pathologies.

Therapeutic Ultrasound as a Treatment Modality for Physiological and Pathological Ageing Including Alzheimer's Disease

Physiological and pathological ageing (as exemplified by Alzheimer's disease, AD) are characterized by a progressive decline that also includes cognition. How this decline can be slowed or even reversed is a critical question. Here, we discuss therapeutic ultrasound as a novel modality to achieve this goal. In our studies, we explored three fundamental strategies, (i) scanning ultrasound on its own (SUS^only), (ii) therapeutic ultrasound in concert with intravenously injected microbubbles (which transiently opens the blood-brain barrier, SUS^+MB), and (iii) SUS^+MB in combination with therapeutic antibodies (SUS^+MB+mAb). These studies show SUS^+MB effectively clears amyloid and restores memory in amyloid-depositing mice and partially clears Tau and ameliorates memory impairments in Tau transgenic mice, with additional improvements found in combination trials (SUS^+MB+mAb). Interestingly, both SUS^only and SUS^+MB restored the induction of long-term potentiation (LTP, electrophysiological correlate of memory) in senescent wild-type mice. Both lead to increased neurogenesis, and SUS^only, in particular, resulted in improved spatial memory. We discuss these findings side-by-side with our findings obtained in AD mouse models. We conclude that therapeutic ultrasound is a non-invasive, pleiotropic modality that may present a treatment option not only for AD but also for enhancing cognition in physiological ageing.

Innovative Applications of MR-Guided Focused Ultrasound for Neurological Disorders

Magnetic resonance-guided focused ultrasound (MRgFUS) is a cutting-edge technology that is changing the practice of movement disorders surgery. Given the noninvasive and innovative nature of this technology, there is great interest in expanding the use of MRgFUS to additional diseases and applications. Current approved applications target the motor thalamus to treat tremor, but clinical trials are exploring or plan to study noninvasive lesions with MRgFUS to ablate tumor cells in the brain as well as novel targets for movement disorders and brain regions associated with pain and epilepsy. Although there are additional potential indications for lesioning, the ability to improve function by destroying parts of the brain is still limited. However, MRgFUS can also be applied to a brain target after intravenous delivery of microbubbles to create cavitations and focally open the blood-brain barrier (BBB). This has already proven to be safe and technically feasible in human patients with Alzheimer's disease, and this action alone has potential to clear extracellular pathology associated with this and other neurodegenerative disorders. This also provides a foundation for noninvasive intravenous delivery of therapeutic molecules to precise brain targets after transient disruption of the BBB. Certain chemotherapies for brain tumors, immunotherapies, gene, and cell therapies are all examples of therapeutic or even restorative agents that normally will not enter the brain without direct infusion but which have been shown in preclinical studies to effectively traverse the BBB after transient disruption with MRgFUS. Here we will review these novel applications of MRgFUS to provide an overview of the extraordinary potential of this technology to expand future neurosurgical treatments of brain diseases.

Transcriptomic response of brain tissue to focused ultrasound-mediated blood-brain barrier disruption depends strongly on anesthesia

Focused ultrasound (FUS) mediated blood-brain barrier disruption (BBBD) targets the delivery of systemically-administered therapeutics to the central nervous system. Preclinical investigations of BBBD have been performed on different anesthetic backgrounds; however, the influence of the choice of anesthetic on the molecular response to BBBD is unknown, despite its potential to critically affect interpretation of experimental therapeutic outcomes. Here, using bulk RNA sequencing, we comprehensively examined the transcriptomic response of both normal brain tissue and brain tissue exposed to FUS-induced BBBD in mice anesthetized with either isoflurane with medical air (Iso) or ketamine/dexmedetomidine (KD). In normal murine brain tissue, Iso alone elicited minimal differential gene expression (DGE) and repressed pathways associated with neuronal signaling. KD alone, however, led to massive DGE and enrichment of pathways associated with protein synthesis. In brain tissue exposed to BBBD (1 MHz, 0.5 Hz pulse repetition frequency, 0.4 MPa peak-negative pressure), we systematically evaluated the relative effects of anesthesia, microbubbles, and FUS on the transcriptome. Of particular interest, we observed that gene sets associated with sterile inflammatory responses and cell-cell junctional activity were induced by BBBD, regardless of the choice of anesthesia. Meanwhile, gene sets associated with metabolism, platelet activity, tissue repair, and signaling pathways, were differentially affected by BBBD, with a strong dependence on the anesthetic. We conclude that the underlying transcriptomic response to FUS-mediated BBBD may be powerfully influenced by anesthesia. These findings raise considerations for the translation of FUS-BBBD delivery approaches that impact, in particular, metabolism, tissue repair, and intracellular signaling.

A comparative study of the effects of Aducanumab and scanning ultrasound on amyloid plaques and behavior in the APP23 mouse model of Alzheimer disease

BACKGROUND

Aducanumab is an anti-amyloid-β (Aβ) antibody that achieved reduced amyloid pathology in Alzheimer's disease (AD) trials; however, it is controversial whether it also improved cognition, which has been suggested would require a sufficiently high cumulative dose of the antibody in the brain. Therapeutic ultrasound, in contrast, has only begun to be investigated in human AD clinical trials. We have previously shown that scanning ultrasound in combination with intravenously injected microbubbles (SUS), which temporarily and safely opens the blood-brain barrier (BBB), removes amyloid and restores cognition in APP23 mice. However, there has been no direct testing of how the effects of SUS compare to immunotherapy or whether a combination therapy is more effective.

METHODS

In a study comprising four treatment arms, we tested the efficacy of an Aducanumab analog, Adu, both in comparison to SUS, and as a combination therapy, in APP23 mice (aged 13-22 months), using sham as a control. The active place avoidance (APA) test was used to test spatial memory, and histology and ELISA were used to measure amyloid. Brain antibody levels were also determined.

RESULTS

We found that both Adu and SUS reduced the total plaque area in the hippocampus with no additive effect observed with the combination treatment (SUS + Adu). Whereas in the cortex where there was a trend towards reducing the total plaque area from either Adu or SUS, only the combination treatment yielded a statistically significant decrease in total plaque area compared to sham. Only the SUS and SUS + Adu groups included animals that had their plaque load reduced to below 1% from above 10%. There was a robust improvement in spatial memory for the SUS + Adu group only, and in this group the level of Adu, when measured 3 days post-treatment, was 5-fold higher compared to those mice that received Adu on its own. Together, these findings suggest that SUS should be considered as a treatment option for AD. Alternatively, a combination trial using Aducanumab together with ultrasound to increase brain levels of the antibody may be warranted.

Modeling Pharmacokinetics and Pharmacodynamics of Therapeutic Antibodies: Progress, Challenges, and Future Directions

With more than 90 approved drugs by 2020, therapeutic antibodies have played a central role in shifting the treatment landscape of many diseases, including autoimmune disorders and cancers. While showing many therapeutic advantages such as long half-life and highly selective actions, therapeutic antibodies still face many outstanding issues associated with their pharmacokinetics (PK) and pharmacodynamics (PD), including high variabilities, low tissue distributions, poorly-defined PK/PD characteristics for novel antibody formats, and high rates of treatment resistance. We have witnessed many successful cases applying PK/PD modeling to answer critical questions in therapeutic antibodies’ development and regulations. These models have yielded substantial insights into antibody PK/PD properties. This review summarized the progress, challenges, and future directions in modeling antibody PK/PD and highlighted the potential of applying mechanistic models addressing the development questions.

Tau antibody isotype induces differential effects following passive immunisation of tau transgenic mice

One of the main pathological hallmarks of Alzheimer's disease (AD) is the intraneuronal accumulation of hyperphosphorylated tau. Passive immunotherapy is a promising strategy for the treatment of AD and there are currently a number of tau-specific monoclonal antibodies in clinical trials. A proposed mechanism of action is to engage and clear extracellular, pathogenic forms of tau. This process has been shown in vitro to be facilitated by microglial phagocytosis through interactions between the antibody-tau complex and microglial Fc-receptors. As this interaction is mediated by the conformation of the antibody's Fc domain, this suggests that the antibody isotype may affect the microglial phagocytosis and clearance of tau, and hence, the overall efficacy of tau antibodies. We therefore aimed to directly compare the efficacy of the tau-specific antibody, RN2N, cloned into a murine IgG1/κ framework, which has low affinity Fc-receptor binding, to that cloned into a murine IgG2a/κ framework, which has high affinity Fc-receptor binding. Our results demonstrate, for RN2N, that although enhanced microglial activation via the IgG2a/κ isotype increased extracellular tau phagocytosis in vitro, the IgG1/κ isoform demonstrated enhanced ability to reduce tau pathology and microgliosis following passive immunisation of the P301L tau transgenic pR5 mouse model.

Recent Strategies for Targeted Brain Drug Delivery

Because the brain is the most important human organ, many brain disorders can cause severe symptoms. For example, glioma, one type of brain tumor, is progressive and lethal, while neurodegenerative diseases cause severe disability. Nevertheless, medical treatment for brain diseases remains unsatisfactory, and therefore innovative therapies are desired. However, the development of therapies to treat some cerebral diseases is difficult because the blood-brain barrier (BBB) or blood-brain tumor barrier prevents drugs from entering the brain. Hence, drug delivery system (DDS) strategies are required to deliver therapeutic agents to the brain. Recently, brain-targeted DDS have been developed, which increases the quality of therapy for cerebral disorders. This review gives an overview of recent brain-targeting DDS strategies. First, it describes strategies to cross the BBB. This includes BBB-crossing ligand modification or temporal BBB permeabilization. Strategies to avoid the BBB using local administration are also summarized. Intrabrain drug distribution is a crucial factor that directly determines the therapeutic effect, and thus it is important to evaluate drug distribution using optimal methods. We introduce some methods for evaluating drug distribution in the brain. Finally, applications of brain-targeted DDS for the treatment of brain tumors, Alzheimer's disease, Parkinson's disease, and stroke are explained.

Single-cell mapping of focused ultrasound-transfected brain

Gene delivery via focused ultrasound (FUS) mediated blood-brain barrier (BBB) opening is a disruptive therapeutic modality. Unlocking its full potential will require an understanding of how FUS parameters (e.g., peak-negative pressure (PNP)) affect transfected cell populations. Following plasmid (mRuby) delivery across the BBB with 1 MHz FUS, we used single-cell RNA-sequencing to ascertain that distributions of transfected cell types were highly dependent on PNP. Cells of the BBB (i.e., endothelial cells, pericytes, and astrocytes) were enriched at 0.2 MPa PNP, while transfection of cells distal to the BBB (i.e., neurons, oligodendrocytes, and microglia) was augmented at 0.4 MPa PNP. PNP-dependent differential gene expression was observed for multiple cell types. Cell stress genes were upregulated proportional to PNP, independent of cell type. Our results underscore how FUS may be tuned to bias transfection toward specific brain cell types in vivo and predict how those cells will respond to transfection.

Clinically approved IVIg delivered to the hippocampus with focused ultrasound promotes neurogenesis in a model of Alzheimer's disease

Preclinical and clinical data support the use of focused ultrasound (FUS), in the presence of intravenously injected microbubbles, to safely and transiently increase the permeability of the blood-brain barrier (BBB). FUS-induced BBB permeability has been shown to enhance the bioavailability of administered intravenous therapeutics to the brain. Ideal therapeutics candidates for this mode of delivery are those capable of inducing benefits peripherally following intravenous injection and in the brain at FUS-targeted areas. In Alzheimer's disease, intravenous immunoglobulin (IVIg), a fractionated human blood product containing polyclonal antibodies, act as immunomodulator peripherally and centrally, and it can reduce amyloid pathology in the brain. Using the TgCRND8 mouse model of amyloidosis, we tested whether FUS can improve the delivery of IVIg, administered intravenously (0.4 g/kg), to the hippocampus and reach an effective dose to reduce amyloid plaque pathology and promote neurogenesis. Our results show that FUS-induced BBB permeability is required to deliver a significant amount of IVIg (489 ng/mg) to the targeted hippocampus of TgCRN8 mice. Two IVIg-FUS treatments, administered at days 1 and 8, significantly increased hippocampal neurogenesis by 4-, 3-, and 1.5-fold in comparison to saline, IVIg alone, and FUS alone, respectively. Amyloid plaque pathology was significantly reduced in all treatment groups: IVIg alone, FUS alone, and IVIg-FUS. Putative factors promoting neurogenesis in response to IVIg-FUS include the down-regulation of the proinflammatory cytokine TNF-α in the hippocampus. In summary, FUS was required to deliver an effective dose of IVIg to promote hippocampal neurogenesis and modulate the inflammatory milieu.

Treatment of Alzheimer's Disease and Blood-Brain Barrier Drug Delivery

Despite the enormity of the societal and health burdens caused by Alzheimer's disease (AD), there have been no FDA approvals for new therapeutics for AD since 2003. This profound lack of progress in treatment of AD is due to dual problems, both related to the blood-brain barrier (BBB). First, 98% of small molecule drugs do not cross the BBB, and ~100% of biologic drugs do not cross the BBB, so BBB drug delivery technology is needed in AD drug development. Second, the pharmaceutical industry has not developed BBB drug delivery technology, which would enable industry to invent new therapeutics for AD that actually penetrate into brain parenchyma from blood. In 2020, less than 1% of all AD drug development projects use a BBB drug delivery technology. The pathogenesis of AD involves chronic neuro-inflammation, the progressive deposition of insoluble amyloid-beta or tau aggregates, and neural degeneration. New drugs that both attack these multiple sites in AD, and that have been coupled with BBB drug delivery technology, can lead to new and effective treatments of this serious disorder.

Immune Escape in Glioblastoma Multiforme and the Adaptation of Immunotherapies for Treatment

Glioblastoma multiforme (GBM) is the most frequently occurring primary brain tumor and has a very poor prognosis, with only around 5% of patients surviving for a period of 5 years or more after diagnosis. Despite aggressive multimodal therapy, consisting mostly of a combination of surgery, radiotherapy, and temozolomide chemotherapy, tumors nearly always recur close to the site of resection. For the past 15 years, very little progress has been made with regards to improving patient survival. Although immunotherapy represents an attractive therapy modality due to the promising pre-clinical results observed, many of these potential immunotherapeutic approaches fail during clinical trials, and to date no immunotherapeutic treatments for GBM have been approved. As for many other difficult to treat cancers, GBM combines a lack of immunogenicity with few mutations and a highly immunosuppressive tumor microenvironment (TME). Unfortunately, both tumor and immune cells have been shown to contribute towards this immunosuppressive phenotype. In addition, current therapeutics also exacerbate this immunosuppression which might explain the failure of immunotherapy-based clinical trials in the GBM setting. Understanding how these mechanisms interact with one another, as well as how one can increase the anti-tumor immune response by addressing local immunosuppression will lead to better clinical results for immune-based therapeutics. Improving therapeutic delivery across the blood brain barrier also presents a challenge for immunotherapy and future therapies will need to consider this. This review highlights the immunosuppressive mechanisms employed by GBM cancers and examines potential immunotherapeutic treatments that can overcome these significant immunosuppressive hurdles.

Impact of blood-brain barrier permeabilization induced by ultrasound associated to microbubbles on the brain delivery and kinetics of cetuximab: An immunoPET study using 89Zr-cetuximab

Epidermal growth factor receptor (EGFR), involved in cell proliferation and migration, is overexpressed in ~50% of glioblastomas. Anti-EGFR based strategies using monoclonal antibodies (mAb) such as cetuximab (CTX) have been proposed for central nervous system (CNS) cancer therapy. However, the blood-brain barrier (BBB) drastically restricts their brain penetration which limits their efficacy for the treatment of glioblastomas. Herein, a longitudinal PET imaging study was performed to assess the relevance and the impact of focused ultrasound (FUS)-mediated BBB permeabilization on the brain exposure to the anti-EGFR mAb CTX over time. For this purpose, FUS permeabilization process with microbubbles was applied on intact BBB mouse brain before the injection of ⁸⁹Zr-labeled CTX for longitudinal imaging monitoring. FUS induced a dramatic increase in mAb penetration to the brain, 2 times higher compared to the intact BBB. The transfer of ⁸⁹Zr-CTX from blood to the brain was rendered significant by FUS (k_uptake = 1.3 ± 0.23 min^-1 with FUS versus k_uptake = 0 ± 0.006 min^-1 without FUS). FUS allowed significant and prolonged exposure to mAb in the brain parenchyma. This study confirms the potential of FUS as a target delivery method for mAb in CNS.

Late changes in blood-brain barrier permeability in a rat tMCAO model of stroke detected by gadolinium-enhanced MRI

OBJECTIVES

After cerebral ischaemia the blood-brain barrier (BBB) may be compromised and this has been observed in both clinical and preclinical studies. The timing of BBB disruption after ischaemia has long been considered to be biphasic, however some groups contest this view. Therefore, the purpose of this study was to characterize the BBB permeability timecourse in a rat model at both acute and chronic time points.

METHODS

Unilateral transient middle cerebral artery occlusion (tMCAO) was performed in 15 male Sprague Dawley rats. Change in T1-weighted MR signal before and after an injection of gadolinium-based contrast agent was calculated voxelwise to derive a BBB permeability index (BBBPI) at both early (6 h, 12 h, and 24 h) and late (7 and 14 days) time points.

RESULTS

As expected, BBBPI in the non-lesioned ROI was not significantly different from pre-occlusion baseline at any time point. However, BBBPI in the ipsilateral (lesioned) ROI was statistically different to baseline at day 7 (p < 0.001) and day 14 (p < 0.01) post-tMCAO. There was a small, but not-significant increase in BBBPI in the earlier phase (at 6 hours).

DISCUSSION

Our results indicate a significant late opening of the BBB. This is important as the majority of previous studies have only characterised an early acute BBB permeability in ischemia. However, the later period of increased permeability may indicate an optimal time for drug delivery across the BBB, when it is especially suited to drugs targeting delayed processes.

Secondary effects on brain physiology caused by focused ultrasound-mediated disruption of the blood-brain barrier

Focused ultrasound (FUS) combined with microbubbles is a non-invasive method for targeted, reversible disruption of the blood-brain barrier (FUS-BBB opening). This approach holds great promise for improving delivery of therapeutics to the brain. In order to achieve this clinically important goal, the approach necessarily breaks a protective barrier, temporarily, which plays a fundamental role in maintaining a homeostatic environment in the brain. Preclinical and clinical research has identified a set of treatment parameters under which this can be performed safely, whereby the BBB is disrupted to the point of being permeable to normally non-penetrant agents without causing significant acute damage to endothelial or neuronal cells. Much of the early work in this field focused on engineering questions around how to achieve optimal delivery of therapeutics via BBB disruption. However, there is increasing interest in addressing biological questions related to whether and how various aspects of neurophysiology might be affected when this fundamental protective barrier is compromised by the specific mechanisms of FUS-BBB opening. Improving our understanding of these secondary effects is becoming vital now that FUS-BBB opening treatments have entered clinical trials. Such information would help to safely expand FUS-BBB opening protocols into a wider range of drug delivery applications and may even lead to new types of treatments. In this paper, we will critically review our current knowledge of the secondary effects caused by FUS-BBB opening on brain physiology, identify areas that remain understudied, and discuss how a better understanding of these processes can be used to safely advance FUS-BBB opening into a wider range of clinical applications.